While I include the basic instructions for this process in my book The Conjure Cookbook, I figured I would give a more detailed -- and illustrated -- version of this process.
Now of course, one can often buy ready-made magical washes, but sometimes they are little more than generic perfume with a lot of colorful dyes added. Then of course, one can make their own (particularly if you have access to a good formulary like Conjure Cookbook and thus know your magical recipes.) An obvious way to do this is by adding essential oils to an unscented soap base -- but what can you do if the recipe requires ingredients that don't come in essential or fragrance oil? Many traditional recipes use things like cinquefoil, sugar, bistort and solomon's seal root that aren't exactly fragrant. For these cases, we use the following process:
Step 1: make a nice strong infusion of your herbs. I'd recommend starting with at least 3 cups of water, and simmering it down till you get 1 cup. How much of your herb or spice mixture to use depends a bit on the specific recipe and whether you're going to add any essential oils to the final mix, but just keep in mind you're probably going to get four or more uses from the final mixture and so, try to use enough herbs for four or more occasions.
Step 2: grate up about 1/3 cup of solid castile soap with a cheese grater (or chop it very finely.)
Step 3: to 1 cup of your cooled herbal infusion, add your 1/3 cup grated castile soap. Stir till dissolved.
Step 4: if you are adding any extra essential or fragrance oils to the mixture, now is the time to do so.
Step 5: bottle your mixture in an 8-ounce bottle, and keep it for your use. You may need to shake the mixture before using, as the castile soap can create an interesting pearlescent sediment when left undisturbed. (An old beauty formula called Pearl Water was made in this way.)